Mass concentrations, mass size distributions, time series, and diel variations for organic tracers and major inorganic ions in aerosols from K-puszta, Hungary, during a 2003 summer period are reported. Emphasis was placed on á-/â-pinene secondary organic aerosol (SOA) tracers comprising cis-pinic acid, 3-hydroxyglutaric acid, and 3-methyl-1,2,3-butanetricarboxylic acid. Only cis-pinic acid and the d-limonene SOA tracer 3-carboxyheptanedioic acid exhibited diel variations with highest concentrations at night. Malic acid was fairly well correlated with succinic and oxalic acid, pointing to a similar SOA formation process. No day-night variations were observed for the latter acids, suggesting that they are formed over relatively long time scales. Of the ionic species sulfate, ammonium, and nitrate, only nitrate showed clear diel variations with highest concentrations at night. As to the size-segregated samples, the 2-methyltetrols were present in both the fine and coarse modes, while the C5-alkene triols and the á-/â-pinene SOA tracers were only associated with the fine mode. The ionic species sulfate, ammonium, and nitrate made up for, on average, 24, 10, and 2.6% of the PM2.5 mass, while organic matter was responsible for 47% of that mass. Isoprene and á-pinene secondary organic carbon (SOC) accounted, on average, for, respectively, 6.8 and at least 4.8% of the PM2.5 organic carbon, but the contribution of isoprene SOC was more pronounced during daytime (9.6%), whereas that of á-pinene SOC was largest at night (at least 6.0%).